There are growing fears of a return to civil war in Ethiopia after an offensive by fighters from Tigray into the neighbouring states of Afar and Amhara and the formation of a new rebel alliance aimed at overthrowing the government of the prime minister, Abiy Ahmed.

About 600,000 people died between 2020 and 2022 during a devastating war between the Ethiopian army and the political party and paramilitary group Tigray People’s Liberation Front (TPLF). Both sides are now accusing the other of triggering a return to open conflict.

On Sunday, seven armed groups from around the country, including TPLF, announced the formation of the Ethiopian Peoples’ Forces Alliance for Survival, aimed at deposing the government in Addis Ababa. Then, on Wednesday, TPLF seized control of three airports from federal police. The state-owned carrier, Ethiopian Airlines, said it had suspended flights to the region “due to the current situation”.

TPLF also launched attacks into Afar and Amhara. A humanitarian source in Afar told Agence France-Presse there were heavy artillery attacks by the group on Thursday as they attempted to take control of the town of Yallo, near the Tigrayan border.

Flights to the historic Ethiopian town of Lalibela were also suspended on Thursday because of nearby fighting, while people in Tigray stocked up ⁠on food and cash, with one resident telling Reuters that people there feared they could face siege conditions similar to those during the previous war.

A resident of Adigrat, a city close to the Eritrean border, ‌described panic-buying and shops emptying. “Food shortages are worsening as market shelves sit empty … Essential medicines remain scarce and astronomically expensive,” he told Reuters. “Daily survival has become a constant calculation.”

TPLF’s vice-president, Amanuel Assefa, told AFP: “We are in the situation of full-blown war now.” He confirmed Tigrayan forces were fighting alongside local armed groups in Afar and Amhara.

The group took control of Abala, also on the Tigray-Afar border, on Wednesday, a foreign security source based in Ethiopia told AFP, while a TPLF source said they had seized several other towns in Afar. The foreign security source also said there was fighting around the Amhara town of Weldiya – one of the few routes to the capital, Addis Ababa.

In its first public comments on the fighting, Ethiopia’s army said on ⁠Thursday it had foiled the attacks and killed, wounded or captured more than 500 enemy fighters.

Analysts say TPLF has support from Ethiopia’s​ neighbour and historic adversary Eritrea, which fears landlocked Ethiopia is planning to invade its territory to gain access to the Red Sea. The TPLF’s Assefa told AFP “we have no information about Eritrea’s plan”. Asked if they would request Eritrean intervention, he said: “Not yet.”

The current fighting reflects shifting dynamics from the civil war, when Eritrea and Fano, an insurgent group that is now part of the new alliance, both fought with the government against the Tigrayans.

Speaking at the UN general assembly on Wednesday, the Ethiopian president, Taye Atske-Selassie Amde, decried “the forces of destruction and mayhem” and “interference in our internal affairs by adversarial elements”. He said Ethiopia had exercised “immense restraint” and made progress with its neighbours.

Abiy’s spokesperson, Billene Seyoum, said members of the alliance had been collaborating for a while ​with the financial backing of Eritrea. Eritrea ​has repeatedly denied similar accusations.

TPLF ruled Ethiopia from 1991 to 2018 before being sidelined by the rise of Abiy, eventually triggering the civil war.

The renewed fighting marks the most serious challenge ​yet to the 2022 Pretoria agreement, which ended the civil war and maintained an uneasy calm until late last year, when clashes resumed.

It raises fears of a broader regional conflict that could draw in armed groups from across and further destabilise a region already strained by war in neighbouring Sudan and tensions along the Red Sea.

On Wednesday, the African Union chair, Mahmoud Ali Youssouf, urged “utmost restraint” from the warring parties and resumption of direct talks. An EU spokesperson called for “immediate de-escalation” and a recommitment to the Pretoria agreement.

In the 2020-22 war, Tigray was largely cut off from the outside world as communications were severed, and access to food, cash and medicines was severely restricted, pushing hundreds of thousands of people into famine-like conditions.

AFP and Reuters contributed reporting